For many years there have been attempts to devise adhesives that possess electrical conductivity, and numerous U.S. patents have been issued on such products, representative examples of which will now be mentioned For example, U.S. Pat. No. 3,347,978 discloses electrically conductive joints and gaskets where an adhesive containing a mass of electrically conductive fibers is used to bond two metal members. U.S. Pat. No. 4,008,300 discloses a foraminous elastomeric film in which the perforations are filled with a hardened electrically conductive adhesive slurry that bulges beyond both faces of the elastomer. In the field of pressure-sensitive adhesives (PSAs), U.S. Pat. No. 2,822,509 discloses an adhesive plaster having a conductive backing and an adhesive containing conductive particles. U.S. Pat. Nos. 3,762,946 and 4,548,862 teach the incorporation of chains of electrically conductive particles extending between the faces of a PSA layer. U.S. Pat. No. 4,606,962 describes a pressure-sensitive adhesive layer incorporating conductive metal-coated particles, somewhat thicker than the adhesive layer. U.S. Pat. No. 4,457,796 discloses a PSA transfer adhesive containing chopped metal fibers to impart localized electrical conductivity.
Where it is important to have an adhesive that possesses both good electrical conductivity and good adhesion, most of the adhesive constructions discussed in the preceding paragraph have been confronted by a serious problem. If a large quantity of conductive particles or fibers is blended with the adhesive, electrical conductivity is excellent, but adhesive properties are significantly reduced. On the other hand, if a small quantity of conductive fibers or particles is incorporated in the adhesive, adhesion properties may be adequate but electrical conductivity is often too low to be acceptable for the intended use. The foregoing problem is exacerbated as the adhesive layer increases in thickness.
In the manufacture of refrigerators, washing machines, dryers, and the like, metal panels are typically spot welded or riveted together to form the enclosure for the appliance. While these methods of joining the panels provide both mechanical strength and electrical continuity, skilled operators are required, and the inevitable disruption of the metal surface requires an abrading operation to restore adequate smoothness. It has been recognized that an aggressive adhesive construction having excellent electrical conductivity would be more convenient to use, but no such adhesive construction has heretofore been available.